The present invention relates to heavy-current electrical engineering and, more particularly, to a carbon-graphite material for brushes of electric machines.
Improving the reliability and, at the same time, reducing the specific gravity of active electrotechnical materials, particularly by increasing rotation speeds along with increasing working temperatures of the windings, is one of the current trends in perfecting electric machines. In the case of commutator machines, serious difficulties are encountered, especially providing for sufficiently reliable commutation and wear resistance of the sliding contact pair of the machines.
Enhancing the performance of a brush contact operating at a temperature higher than 150.degree. C., the point at which adsorption of water vapors from the ambient atmosphere by the rubbing contact surfaces becomes minimum, is quite a big problem.
Improving the properties of a carbon-graphite material through impregnation thereof in various impregnating compounds is one of the ways to eliminate the above difficulties.
A great number of formulations for impregnating compounds have been disclosed in patents issued in many countries and, in particular, known in the art are compounds based on drying vegetable oils, various resins and other organic and inorganic chemicals.
For example, such patents have been granted for applications of the Federal Republic of Germany (Nos. 1,091,218 and 1,241,903), France (No. 1,005,261), the USA (Nos. 2,989,490 and 2,425,046 etc.). However, more thorough analysis and studies conducted in the USSR have shown that the known formulations for impregnating compounds and their additives, increase the durability of electric brushes without taking into account special operating conditions by 2-3 times on the average and are suitable for operation at a working temperature ranging from 200.degree. to 250.degree. C.
The nearest analogue to the subject of the present invention is British Pat. No. 823,964 which discloses a carbon-graphite brush material containing sodium pyrophosphate and a solidified mixture of unsaturated resins (polyesters).
The brushes described in the British patent are intended for operation under heavy conditions and at high altitude.
However, this material fails to provide for satisfactory operation of brushes within a wide range of temperatures, the reason being that sodium pyrophosphate, just as phosphates of light metals in general, disintegrate relatively fast.